This paper gives an analytic description of why and how an instructional writing program on the improvement of cross-genre writing skills in German secondary grade level has been designed and implemented. From a diagnostic research phase, and according to theoretical expectations, coherence management and perspective taking proved to be ability components that substantially contribute to text quality across different genres. To train these two abilities in a didactical setting, two 11-unit writing courses were analogously constructed and administered in 5th and 9th grades. There were 12 intervention classes and 12 control classes in each grade, forming 48 classes with 1.145 participants. The decisions that lead to the design of the intervention study and the corresponding didactical settings are explained and justified in detail, and the developed self-learning materials are described in terms of their assumed learning potentials and the underlying didactical principles. Based on the obtained empirical experiences, the intervention is critically evaluated with respect to good intervention research and its proper description.